Simply put I would say the Atheist has no rational or logical way to formulate an actual moral or ethic, from a reality standpoint.

While it's possible for him or her to imagine or perceive such a thing, there is simply no way in reality this is possible. I can easily developed that point.

In the first place, this is not a moral it's an Instinct, any animal can avoid pain or misery. It takes no thinking process.

Secondly, since according to the Naturalistic proposition, much animal life existed before the human brain, it would follow that pain or misery and it's avoidance was not invented as a moral by the human mind, therefore not an actual moral or ethic. The lion and Bear do not share your opinion,when they are on the giving end of misery. We only discovered that it's a thing to avoid as well, for natural reasons, not ethical ones.

Thirdly, since I can get very different responses from human minds as to what constitutes a moral or immoral act, it should be immediately evident that there is no way to establish OBJECTIVELY, from a Naturalistic standpoint, what is in REALITY morally real.

Therefore, it is logically impossible for an actual ethic or moral to exist from the Atheistic standpoint, in Reality.